US3776247A

US3776247A - Process for the preparation of a crude-oil composition with a depressed pour point

Info

Publication number: US3776247A
Authority: US
Inventors: J Choufoer; Kerkvoort W Van; Der Meij P Van; T Schrueder
Original assignee: Shell Oil Co
Current assignee: Shell USA Inc
Priority date: 1967-07-07
Filing date: 1968-07-01
Publication date: 1973-12-04
Anticipated expiration: 1990-12-04
Also published as: GB1161188A; IE32096B1; IE32096L; NO127015B; SU365898A3; DE1770695A1; SE355377B; BE717234A; FI51712B; AT289993B; FI51712C; OA02849A; FR1575984A; CA980118A; DK138374B; YU138868A; ES355848A1; NL6709453A; CH496794A; DK138374C

Abstract

A method of transporting waxy crudes through conduits at reduced friction and preventing wax separation or precipitation so as to inhibit plugging and flow restriction and improve the pour point properties of the crude by adding to such waxy crudes a small amount of a polymeric material containing aliphatic hydrocarbon side chains of at least 14 carbon atoms. This invention relates to decreasing friction loss in flowing waxy crudes through conduits, generally over great distances but also over short distances such as in well fracturing processes and also to improving the pour point of waxy crudes. More particularly, the invention is directed to crude oil compositions comprising a waxy crude oil and fractions thereof and polymers having aliphatic hydrocarbon side chains with at least 14 carbon atoms, so as to reduce the pour point, prevent wax separation and reduce its friction loss due to flow through pipelines over great distances and short distances.

Description

United States Patent [1 1 Choufoer et a1.

[451 Dec. 4,1973

[ PROCESS FOR THE PREPARATION OF A CRUDE-OIL COMPOSITION WITH A DEPRESSED POUR POINT [75] Inventors: Johannes I'I. Chouioer; Willem J.

Van Kerkvoort; Pieter H. Van der Meij; Thomas Schrueder, all of Amsterdam, Netherlands [30] Foreign Application Priority Data July 7, 1967 Netherlands .1 6709453 [52] US. Cl 137/13, 44/62, 44/70, 44/80 [51] Int. Cl Fl7d 1/16, C101 1/18 [58] Field of Search 44/51, 62, 70, 80; 137/13 [56] References Cited UNITED STATES PATENTS 3,445,205 5/1969 Patinkin et a1 44/62 3,447,915 6/1969 Otto 44/62 3,462,249 8/1969 Tunkel 44/62 3,248,186 4/1966 Brownawell et al. 44/62 3,576,639 3/1971 Aaron et a1 44/62 X 3,449,251 6/1969 Tunkel et al 44/62 X FOREIGN PATENTS OR APPLICATlONS 6,603,483 9/1967 Netherlands 44/62 Primary Examiner-Daniel E. Wyman Assistant Examiner-W. J. Shine Attorney-George G. Pritzker and J. H. McCarthy [57 ABSTRACT A method of transporting waxy crudes through conduits at reduced friction and preventing wax separation or precipitation so as to inhibit plugging and flow restriction and improve the pour point'properties of the crude by adding to such waxy crudes a small amount of a polymeric material containing aliphatic hydrocarbon side chains of at least 14 carbon atoms.

This invention relates to decreasing friction loss in flowing waxy crudes through conduits, generally over great distances but also over short distances such as in well fracturing processes and also to improving the pour point of waxy crudes. More particularly, the invention is directed to crude oil compositions comprising a waxy crude oil and fractions thereof and polymers having aliphatic hydrocarbon side chains with at least 14 carbon atoms, so as to reduce the pour point, prevent wax separation and reduce its friction loss due to flow through pipelines over great distances and short distances.

6 Claims, No Drawings PROCESS FOR THE PREPARATION OF A CRUDE-OIL COMPOSITION WITH A DEPRESSED' POUR POINT BACKGROUND OF THE INVENTION Dependent on the field of production, crude oils may contain considerable quantities of wax. This wax gradually separates when the oil is cooled to below a certain temperature. The coherence of the separated wax crystals in spatial structures imparts a certain stifiness to the oil. At sufficiently low temperatures the oil may even completely solidify. As will be explained below, the presence of crystallized wax in crude oil has a detrimental effect on the flow properties and handleability of the oil.

When crude oil is produced from a well which passes through strata of lower temperatures than that of the oil-bearing formation, the oil coming into contact with the cold wall of the well may stiffen, which interferes with its transport to the surface. If production -is temporarily interrupted, the oil may even solidify completely,

which involves serious problems when production is resumed.

When oil is stored in tanks which are not provided with heating facilities or insulation, the oil in contact with the cold walls and bottom of the tank will cool down and, as a result, may stiffen. This leads to difficulties in pumping the oil from the tank; infact, considerable quantities of stiffened oil may thus remain behind, which reduces the effective capacity of thetank.

This problem acquires even greater importance during transport of waxy crude oil 'in unheated tankers, where the walls of the compartments are partly formed by the ships hull, which is in direct contact with the cold sea water. Large quantities of stiffened oil remaining behind when the tanker is discharged, reduce the carrying capacity of the ship; in addition, subsequent cargoes of crude oil may become contaminated.

The poorer flow properties of the oil at lower temper ature will also considerably interfere with the transport of the oil through a pipeline, either by pumping or by flow under the influence of prevailing pressure or level difi'erences.

When waxy crude oils are pumped through a pipeline, high flow resistances may build up, thus calling for settling, centrifuging, filtration or coalescence, require the'oil to be thin-liquid. If, owing to the presence of crystallized wax, the flow of the oil is insufficient, there is a possibility that these operations cannot be carried out at all or only to a limited extent.

Good flow properties of a crude oil are desired not only for transport and storage, but also for many other reasons. In this connection, for example, mention may be made of sampling, the transmittance of pressure signals through narrow lines and the proper functioning of automatic equipment installed in refineries and along pipelines for purposes such as temperature and density measurements.

As-appears from the above, the flow properties of a crude oil play a great part both during production and upon storage, transport and refining of the oil. It is therefore very important to minimize the adverse effect of wax on the flow properties of the oil.

To predict the flow behaviour of a crude oil under operational conditions, laboratory-scale measurements are carried out of quantities which may be regarded as characteristic of the flow behaviour of the oil, viz. pour point, viscosity and yield stress. The pour point is a criterion of the lowest permissible temperature during storage or transport or during a possible interruption of transport. The 'yield stress gives an impression of the shear stresses which may be expected if a stagnant oil is to be set in motion again. The viscosity is particularly related to the resistance which the oil experiences during pumping.

In general, it may be said that according as a crude oil has a lower pour point, a lower yield stress and a a very high pump power. This may lead to high cost of transport, particularly in long-distancepipelines. If the resistance is very high, the available discharge pressure of the pump or the maximum permissible pressure determined by the strength of the pipe may be insufficient, so that the crude oil cannot be pumped.

If pumping is interrupted while the waxy crude oil is in the pipeline, the oil, which is often warmer than the surroundings, will cool down. The'wax separated during cooling can freely form a spatial structure,'which may extend over the entire cross section of the pipe and requires a very high pumppressure to be broken. If this pressure exceeds the available or permissible discharge, pressure, transport cannot be resumed.

When a waxy crude is pumped through a pipeline as well as when it remains still, the oil may solidify on the cold pipe wall to form a deposit, which remains behind. This reduces the capacity of the pipeline and entails the risk of contamination of subsequent batches of crude oil which have to be pumped through the pipeline.

Certain operations of crude oil refining, such as separation of water or sediment, for example by means of lower viscosity, it will better handleable in practice. It. is well known in the 'art that friction resulting in the transportation of hydrocarbon liquids, ranging in viscosity from gasoline to also waxy crude oils transported through pipelines, contributes greatly to pumping costs due to increasing energy requirements necessary to overcome frictional increases due to wax depositions which can ultimatelyseriously damage the pipelines.

To reduce friction and overcome the undesired effects mentioned above, various means have been tried such as coating of the pipe walls with friction reducing materials or by addition of friction reducing chemical agents to the transported liquids such as described in 'U. S. Pat. Nos. 2,492,173; 3,023,760; 3,102,548 and 3,215,154. However, these means of reducing friction have met with little success because of the high cost of either coating the pipe walls or that of the friction reducing chemical agents.

SUMMARY OF THE INVENTION It has now been found that the flow properties of waxy crude oils can be improved in a simple manner by adding to the oil a small quantity of polymeric compounds with a special structure. For, it has appeared that polymers containing aliphatic hydrocarbon side chains with at least 14 carbon atoms and which polymers may be regarded as having been obtained by polymerization of olefinically unsaturated compounds, are even at a low concentration capable of effecting a considerable reduction in pour point, yield stress and viscosity of waxy crude oils. i

The invention therefore relates to a crude oil composition comprising a waxy crude oil and polymers containing aliphatic hydrocarbon side chains with at least 14 carbon atoms, which polymers may be taken to have been obtained by polymerization of olefinically unsaturated compounds.

For the sake of brevity the terms "long hydrocarbon chains" and long hydrocarbon side chains will be used hereinafter to designate aliphatic hydrocarbon chains and aliphatic hydrocarbon side chains with at least 14 carbon atoms, respectively.

As the polymers according to the invention are capable of improving the flow properties of waxycrude oils, the afore-mentioned problems, which arise during production, storage, transport and refining of waxy crude oils owing to insufficient flow, can be effectively solved by incorporating these polymers into the waxy crude oil. Some aspects of the invention will be further discussed hereinafter.

When waxy crude oil is shipped, it is customary to keep the cargo during transport at an elevated temperature, for example by means of steam coils. The invention offers the possibility of shipping waxycrude oils without heating during the voyage being necessary. This means not only an appreciable saving for existing tankers, where the available energycan then be fully utilized to propel the ship, but particularly when constructing new tankers, where the installation of costly equipment for heating the cargo can be omitted. In spite of the cold shipment a low tum-out loss can be maintained. Shipment of unheated waxy crude oil containing polymers according to the invention permits the use of higher discharge pumping rates.

One of the most serious interruptions which may occur during transport of crude oil through a pipeline is line blocking after pumping at low temperatures or after the oil in the line having remained still. This risk is by no means imaginary, particularly when waxy crude oils are pumped. In this connection crude oils to be transported through pipelines have to meet stringent requirements as regards flow properties. It was for this reason that in the past various waxy crude oils were 'rejected for pipeline transport, so that these oils had to be transported in a different way. The present invention, which aims at improving the flow properties of waxy crude oils, is preeminently suitable considerably to reduce any risks during transport of such oils. The invention not only presents the possibility of reducing the required pump power, which'will reduce the cost of pumping, but by applying the invention the transport capacity of the line may be increased at the same pump power. Waxy crude oils which up to now were regarded as unacceptable for pipeline transport because of their flow properties, can now be rendered suitable for this,

purpose by applying the invention.

In comparison with known techniques to render waxy crude oils suitable for pipeline transport, which involve dilution of the waxy crude oil with a relatively large quantity of a thin-liquid oil with a low wax content, the present methodhas the advantage that, since only very residue. This is an important aspect of the invention, as these residues are employed, for instance, as fuel oil for heating purposes and as fuel for low-speed diesel engines. In these applications the flow properties play a very important part.

In order to be suitable for application according to the invention, the polymers'should contain long hydrocarbon side chains with at least 14 carbon atoms. Preferred are polymers wherein the long hydrocarbon side chains are unbranched and saturated, that is, polymers in which the long hydrocarbon, side chains can be represented by the formula CH (CH ),,CH in which n 2 12. For practical applications, preferably polymers are chosen with long hydrocarbon side chains, wherein the number of carbon atoms is at least 16 and at most 30, in particular at least 18 and at most The polymers that may be employed as pour point depressants according to the invention consist of a main chain built up of carbon atoms, which main chain carries long hydrocarbon side chains. These long hydrocarbon side chains may be attached either directly or indirectly to the main chain. In the former case there are no further atoms between the first carbon atom of the long hydrocarbon side chain and the carbon atom of the main chain to which the side chain is attached. If the long hydrocarbon side chain is attached indirectly to the main chain, one or more other atoms such as carbon, oxygen, sulphur,-nitrogen or phosphorus atoms are present between the first carbon atom of the long hydrocarbon side chain and the carbon atom of the main chain to which the side chain is attached. Preference is given to polymers wherein the long hydrocarbon side chains are attached indirectly to the main chain, via one or more oxygen and/or carbon atoms. Some examples of polymers wherein the aliphatic hydrocarbon side chains are attached indirectly to the main chain via one or more oxygen and/or carbon atoms are-polymers-wherein the aliphatic hydrocarbon side chains are attached to the main chain via a carboxyl group or via an oxygen atom, or via at least two carbon atoms of an aromatic ring system.

The preparation of such polymers may basically be carried out in two manners. In the first place, these polymers can be prepared by polymerization of olefinically unsaturated compounds, of which at least a proportion consists of olefinically unsaturated compounds containing, in addition to a polymerizable C=C group, a long hydrocarbon chain. Olefinically unsaturated compounds of this type will hereinafter be termed olefinically unsaturated compounds containing a long hydrocarbon chain. A second manner in which these small quantities of polymer are necessary to re'achthe polymers can be prepared is by polymerization of olefinically unsaturated compounds containing no long hydrocarbon'chain and aftertreatment of the polymer, by means of which these long hydrocarbon chains are introduced into the polymer as side chains.

The polymers applicable as pour point depressants according to the invention may be either homopolymers or copolymers.

If the preparation is carried out by direct polymerization, that is, without an after-treatment, the material to be polymerized should invariably contain olefinically unsaturated compounds with long hydrocarbon chains. When homopolymers are prepared in this manner, the starting material is one specific olefinically unsaturated monomer with a long hydrocarbon chain. When copolymers are prepared in this manner, the starting material is a monomer mixture which, in addition to a specific olefinically unsaturated monomer with a long hydrocarbon chain, contains one or more other monomers which may or may not contain a long hydrocarbon chain.

If the preparation is carried out by indirect polymerization, i.e., including an after-treatment, the material to be polymerized need not contain any olefinically unsaturated compounds with long hydrocarbon chains. When homopolymers are prepared in this manner, the starting material is one specific olefinically unsaturated monomer from which a polymer can be prepared that is suitable for the desired after-treatment. When co-" polymers are thus prepared, thestarting material is, for example, a mixture of monomers, which, in addition to one specific monomer from which a polymer can be prepared that is suitable for the desired aftertreatment, contains one or more other monomers which may or may not contain a long hydrocarbon chain.

The molecular weight of the polymers applicable as flow improvers of the invention may vary between wide limits. For application in practice it is preferable to choose polymers whose average molecular weight (number of average M ranges between 1,000 and 1,000,000, in particular between 4,000and 100,000.

Depending upon the nature of the parafi'in waxes present in the crude oil, it may be preferable to incorporate in this crude oil polymers of the invention, wherein the long hydrocarbon side chains differ in chain length by a number of carbon atoms.

Some examples of olefinically unsaturated compounds containing long hydrocarbon chains, suitable for the preparation of the polymers according to the invention, are vinyl esters and allyl esters of saturated monocarboxylicacids, such as vinyl esters and al'lyl esters of arachidic acid and behenic acid; alkyl esters of unsaturated monocarboxylic acids, such as n-octad'ecyl acrylate and n-eicosyl methacrylate alkyl amides of unsaturated monocarboxylic acids such as n-eicosyl acrylamide and n-docosyl methacrylamide; dialkyl esters of unsaturated dicarboxylic acids, such as di-noctadecyl maleate and di-n-tetracosyl fumarate; dialkylamides of unsaturated dicarboxylic acids, such as din-eicosylmaleic diamide and di-n-docosylfumaric diamide; imides of unsaturated dicarboxylic acids, such as n-octadecylmaleic acid imide and n-eicosylmaleic acid imide; alkyl vinyl ethers,.such as n-docosylvinyl ether and n-tetracosyl vinyl ether and mono-olefins such as l-octacosene and l-docosene and olefinically unsaturated aromatic compounds, such as alkylstyrenes, acylstyrenes, alkylhydroxystyrenes, alkylcarboxystyrenes, alkyloxystyrenes, alkylamidostyrenes, alkylvinylnaphthalenes and acylvinylnaphthalenes.

Some examples of olefinically unsaturated compounds which have no long hydrocarbon chains and by means of which the compounds which do possess such long hydrocarbon chains can be copolymerized are, for instance, vinyl esters of unsaturated monocarboxylic acids, such as vinyl acetate; alkyl esters of unsaturated mono and dicarboxylic acids, such as methyl methacrylate and diethyl maleate, alkyl vinyl ethers, such as octyl vinyl ether; mono-oletms, such as ethane and isobutene and aromatic compounds, such as styrene, a-methylstyrene and vinylnaphthalene.

Some examples of polymers'obtained by direct polymerization of olefinically unsaturated compounds of which at least a proportion consists of olefinically unsaturated compounds with long hydrocarbon chains, are, for instance:

Copolymers of vinyl esters of saturated monocarboxylic acids with one another.

Copolymers of vinyl esters of saturated monocarboxylic acids with mono-olefins.

Copolymers of allyl esters of saturated monocarboxylic acids with'one another.

l-lomopolymers of alkyl esters of unsaturated monocarboxylic acids.

Copolymers of alkyl esters of unsaturated monocarboxylic acids with one another.

Copolymers of alkyl esters of unsaturated monocarboxylic acids with dialkyl esters of unsaturated dicarboxylic acids or with mono-olefins.

l-lomopolymers of dialkyl esters of unsaturated dicarboxylic acids.

Copolymers of dialkyl esters of unsaturated dicarboxylic acids with mono-olefins.

Homopolymers of alkyl vinyl ethers.

Copolymers of alkyl vinyl ethers with one another.

' If the polymers are copolymers they may be built up either of two or of more than two different monomers.

Some examples of terpolymers are, for instance, terpolymers obtained by copolymerization of a vinyl ester of a saturated monocarboxylic acid with a dialkyl ester of an unsaturated dicarboxylic acid and a mono-olefin or an alkyl ester of an unsaturated monocarboxylic acid.

Some examples of polymet9 tained by polymerization of olefinically unsaturated compounds containing no long hydrocarbon chains and where, by aftertreatment of the polymer, long hydrocarbon chains are introduced into the polymer as side chains, are, for example: a a

Copolymers of unsaturated monocarboxylic acids, dicarboxylic acids of anhydrides thereof with monoolefins,'vinyl esters of saturated monocarboxylic acids of dialkyl esters of unsaturated dicarboxylic acids, which polymers have been "after-treated with an aliphatic alcohol containing a long hydrocarbon chain.

Homopolymers of unsaturated alcohols; which polymers have been after-treated with an aliphatic carboxylic acid or aliphatic carboxylic chloride containing a long hydrocarbon chain.

Homopolymers of alkyl esters of unsaturated monocarboxylic acids or copolymers of alkyl esters of unsaturated monocarboxylic acids with one another or with monolefins, which polymers have been after-treated with an aliphatic amine containing a long hydrocarbon chain.

Copolymers of anhydrides of unsaturated dicarboxylic acids with mono-olefins or other olefinically unsaturated compounds, which polymers have been aftertreated with an aliphatic amine containing a long hydrocarbon chain.

Homopolymers and copolymers of styrene and substituted styrenes, into which polymers long hydrocarbon chains have been introduced as side chains by means of alkylation or acylation.

Although polymers which contain aliphatic hydrocarbon side chains with at least 14 carbon atoms and which may be taken to have been obtained by polymerization of olefinically unsaturated compounds, are in 7 general suitable for improving the flow properties of waxy crude oils, preference is given to polymers which may be taken to have been obtained by polymerization of olefinically unsaturated compounds which consist at least partly of olefinically unsaturated aliphatic compounds containing a saturated hydrocarbon chain with at least 14 carbon atoms.

Favourable results can be obtained by the application of the polymers mentioned below.

Homoor copolymers of alkyl esters of unsaturated carboxylic acids, such as homoor copolymers of alkyl esters of unsaturated monocarboxylic acids, in particular homoor copolymers of alkyl acrylates. Examples of very suitable homopolymers of alkyl 'acrylates are homopolymers of n-tetradecyl acrylate, homopolymers of n-hexadecyl acrylate, homopolymers of n-octadecyl acrylate and homopolymers of n-eicosyl acrylate.

I Homoor copolymers of alkyl vinyl ethers, in particular homopolymers of n-octadecyl vinyl ether.

Copolymers of a mono-olefin and a dialkyl ester of an unsaturated dicarboxylic acid with at least. 14 carbon atoms in the alkyl groups, in particular'copolymers of ethylene and di-n-octadecyl maleate.

Homoor copolymers of vinylesters of saturated monocarboxylic acids, in particular copolymers of vinyl esters of hydrogenated rape-seed oilfatty acids.

Preference is given to homoor copolymers of alkyl esters of unsaturated carboxylic acids, such as homoor copolymers of alkyl esters of unsaturated monocarboxylic acids, in particular homoor copolymers of alkyl acrylates. Most preferred are homoor copolymers of alkyl acrylates having 18 to 26 carbon atoms in the alkyl group, in particular a homopolymer of noctadecyl acrylate and a homopolymer of n-eicosyl acrylate. 3

The concentration in which the polymers may be applied may vary between wide limits', depending upon the nature, the structure and the molecular weight of the polymer to be employed, the nature of and the quantity of the paraffin waxes present in the crude oil, and the improvement of the flow properties envisaged.

In some instances, a quantity of 0.001 percent w, calculated on the crude oil composition, is already sufficient for attaining the desired improvement in flow properties. in mostcases, a quantity of 2.0 percentgw is amply sufficient.

Preferably, from 0.002 percent w to 0.2 percent w of the polymers is incorporated into the crude oil.

The present polymers have so far been designated in the specification as flow improvers of waxycrude oils. Their features include properties to reduce the pour point, the viscosity and the yield stress of waxy crude oils. With regard to each of these properties: separately they can, if desired, also be designated as pour point depressants, viscosity depressants and yield stress depressants. In this connection it should be observed that a compound may in general be regarded as belonging to the class of pour point depressants only if it is capable of effecting a pour point reduction of at least 6C when it is applied in a concentration of at most 0.2 percent w.

The waxy crude oil to which the polymers according The present polymers, which are particularly important as additives to ease the transport of waxy crude oils through pipelines, by tankers or by other means, can also be very suitably used in oil wells producing waxy crude to prevent the-formation of waxy deposits or to dissolve such deposits formed on the walls of the well.

PREFERRED EMBODIMENT OF THE INVENTION The invention will now be further elucidated with the aid of the following examples.

Seven polymers of the invention have been applied in various different concentrations in the following six crude oils.

Crude Oil I Crude Oil 11 A crude oil originating from South America, with a kinematic viscosity of 1.82 cS at C, a wax content of 17.5 percent w (setting point of the wax 54.5C), a pour point of 26C, determined according to method A, and a pour 'point'of 29C, determined according to method C.

Crude Oil III A crude oil originating from North Africa, with a kinematic viscosity of 5.13 cS at 37.8C, a wax content of 7.0 percent w'(setting point, of the wax 58.0C), a pour point of 4C, determined according to method A, and a pour point of +2C, determined according to method Crude on [V A crude oil originating from North Africa, with a kinematic viscosity of 3.66 cS at 37.8C, a wax content of 7.8 percent w (setting point of the wax 51.5C), a pour point of +2C, determined according to method A, and a pour point of +5C, determined according to method Crude Oil Vv A crude oil originating from West Africa, with a kinematic viscosity of 15.0 cS at 50C, a wax content of 17.8 percent w (setting point of the wax 56.0C), a pour point of 20C, determined according to method B, and a pour point of 32C, determined according to method D.

Crude Oil VI A crude oil originating from West Africa, with a kinematic viscosity of 2.70 cS at 50C, a wax content of 7.0

to the invention may be added, may consist of one waxy percent w (setting point of the wax 54.0C), a pour point of 1 1C, determined according to method A, and a pour point of 14C, determined according to method As regards the methods for the determination of the pour point of waxy crude oils, the following should be pointed out in addition.

The pour point of a waxy crude oil is often dependent upon the thermal pre-treatment to which the oil has been subjected.

On the basis of whether or not a thermal pretreatment is carried out, the methods suitable for the determination of the pour point of waxy crude oils may be divided into two groups, viz.:

1. methods where the pour point is determined on a sample that is not reheated before the determination;

2. methods where the sample is heated to 46C just before the determination.

Although the thermal treatment in some instances results in a higher pour point, it is perhaps less realistic, as the pertaining crude oil is not subjected to this thermal cycle in actual practice.

From the examples in this patent application it appears that the polymers of the invention are capable of depressing the pour point in a general sense, i.e., independent of whether or not the thermal pre-treatment is carried out.

The pour point determination methods A, B, C, and D, mentioned in the examples, were carried out as follows.

METHOD A Two samples of a crude oil are heated to 65C, at which temperature the desired quantity of polymer is added to one of the samples. After cooling the samples to room temperature the pour point is determined as described in ASTM D 97-66/IP /67, but without the reheating to 46C.

METHOD B As described under method A, but in its first line read 100C instead of 65C.

METHOD C Two samples of a crude oil are heated to 65C, at which temperature the desired quantity of polymer is added to one of the samples. After cooling to room temperature the samples are stored at room temperature for at least 24 hours. Subsequently, the pour point is determined as described in ASTM D 97-66/IP 15/67. This pour point is usually specified as the ASTM maximum pour point or the 1? maximum pour point.

METHOD D I As described under method C, but in its first line read 100C instead cf 65C.

The results of the experiments are given in Table I, in which the number of degrees Centigrade is specified at which the pour point determined according to any one of methods A-D is depressed after addition of the various polymers.

For comparison two related polymers (a poly-n-C alkyl methacrylate and a poly n-C alkyl methacrylate) were tested as pour point depressants in crude oil III.

The results of these experiments (with polymers outside the scope of the present invention) are also incorporated in Table I.

YIELD STRESS A sample of crude oil is heated to 65C, at which temperature the desired quantity of polymer is added to the sample. After cooling to room temperature a metal U-tube with a length of 54 cm and an inside diameter of 3.8 mm is filled with the oil to be tested. Subsequently, the oil in the tube is cooled down to the de;

termination temperature, after which the pressure on one of the U-tube limbs is gradually raised.

The pressure (P,,) at which the first flow is observed is used for calculating the yield stress. The yield stress (defined as the shear stress required for setting a congealed oil into motion) is calculated from the observed P with the aid of the equation:

7 P D/4 L,

where:

1', yield stress, dyn/cm 7 P pressure at which the first flow is observed,

D diameter of the tube, cm

L length of the tube, cm

The yield stress of a sample of crude oil VI to which 0.005 percent w of poly n-C alkyl acrylate had been added was determined at two different temperatures in the manner described above, and was compared with the yield stress of a sample of crude oil VI which had been subjected to a similar thermal pre-treatment without any additive. The results obtained are given below: Crude oil VI:

yield stress at 8C: 302 dyn/cm Crude oil VI 0.005 percent w of poly-n-C alkyl acrylate:

yield stress at 8C: 10 dyn/cm .yisli trss at C= 17 i Behaviour During Distillation a maximum vapourtemperature of 300C) from the untreated crude oil and from the two crude oil samples towhich polymer had been added.

The residues showed the following pour points (determined according to ASTM D 97-66).

Residue from untreated crude oil Vl maximum pour point 38C minimum pour point 35C Residue from crude oil VI 0.03%w of poly-n-C alkyl acrylate Residue from crude oil VI 0.03%w of poly-n-C alkyl acrylate maximum pour point 32C minimum pour point l7C maximum pour point 23C minimum pour point l7C VISCOSITY Since waxy crude oils at lower temperatures behave as non-Newtonian liquids, the viscosity of such oils can be determined in a realistic manner only in a viscometer wherein either the shearing stress or the rate of shear can be adjusted between narrow limits and be kept constant. Very suitable for determining viscosities of waxy crude oils is the Ferranti Portable Viscometer, Model VL, a so-called Couette coaxial-cylindrical viscometer of the constant-shear-rate type.

A sample of crude oil is heated to C, at which temperature the desired quantity of polymer is added to the sample. After cooling down to room temperature the reservoir of the viscometer is filled with the oil to be tested.

Note: The yield stress and viscosity (Ferranti viscometer) values for crude oil VII mentioned in this patent application were determined as described on pages 15 and 17 for crude oil VI, but without heating to 65C.

PROPERTIES OF THE DOPED OIL Actual pour point: 2C.

b. Yield stress Test temperature Yield stress c. Viscosity (Ferranti viscometer) rate of a... -s shear.

test sec" 36.9 164 628 temperatue, C 21.4 56 c? 34 cP 32 cP 18.3 82 c? 46 cl 37 c? 15.5 110 cl 52 c? 41 0P 9.7 159 c? 69 CP 47 c? 5.2 223P s7 cP 47 of When the cargo was loaded in North Africa for the 1st voyage, threesamples of crude oil VII were taken.

Two of these samples were doped with polymers according to the invention; the third sample was not doped. The samples were kept in deward, which were stored during the voyage in an insulated wooden case. On arrival in West Europe the samples were stored in a space at a temperature of about 13C. After being stored for about 1 week the yield stress and viscosity of the samples were determined. The results are given below. 1

Sample I: crude oil VII.

Sample 2: crude oil VII 1 0.02 percent w poly-n-C alkyl acrylate.

On arrival of the tanker in West Europe restart trials were made with the doped and the undoped'crude oil in a pipe circuit consisting of 2,000-m 20inch noninsulated pipe and 2,000 m 24 inch insulated pipe. The trials were performed as follows.

The oil undertest was pumped at itstemperature of arrival into the circuit, after which the pump was stopped for some days (shut-in time), so that the oil was allowed to cool down. Subsequently the pressure at the inlet of the circuit was raised by means of a pump in steps until the oil began to flow. The yield stress was calculated from the highest pressure drop over the noninsulated (i.e., cooled) pipe section by means of the afore-mentioned formula:

The results of the restart trials are mentioned below.

Restart Trials with Undoped and Doped Druce undoped doped crude crude Shut-in time, h 78 102 Average temperature non-insulated pipe. "C 9 3 Ambient temperature, C 4 0 Pressure drop in non-insulated pipe, kgf/cm'6.3 0.7S Yield stress related to pipe wall, dyn/cm' 400 47 2nd Voyage 20,000 tons of unheated doped crude oil VII and $30,000 tonsof unheated undoped crude oil VII.

The flow improver used was 0.015 percent w poly-n-C alkyl acrylate.

Temperature during loading in North Africa; 102F Temperature of oiargb' "on arrival in West Europe:

78E. Average rate of cooling: 3F per day.

PROPERTIES OF THE UNDOPED OIL a. Actual pour point: 20C. b. Yield stress Test temperature Yield stress C dyn/cm l7.l' I I8 13.6 302 1 10.4 415 c.-,Viscosity (Ferranti viscometer) rate of shear, test sec 36.9 164 328 temperature, "C 15.0 192 cP 22.7 114 cP 57 GP 45 cP PROPERTIES OF THE DOPED OIL a. Actual pour point: 2C. b. Yield stress Test temperature Yield stress dyn/cm 6.0' 37 L4 76 3.l 206 .c. ViscosityKFerranti viscometer) rate of shear, test sec" 36.9 164 328 temperature, CC V 22.7 37 cl 30 c? 29 cP 10.2 13161 81 cP CE 4.8 210 CP 119 cP 93 cP It was found that the rate of discharge of the doped oil from the tanker was 15 percent higher than that of the undoped oil.

After discharge of the undopedoil stored on arrival in West Europe in unheated floating-roof tanks a solid wax-oil mixture re'mained'behind on the tank wall. This -was not the case with the undoped oil.

The foregoing description of the invention is merely intended to be explanatory thereof. Various changes in g the details of the described method maybe made,

within the scope of the appended claims, without departing from the spirit of the invention.

We claim as our invention:

1. A composition of matter having improved flow and friction-reducing properties comprising 1 a major amount of waxy crude oil having incorporated therein from 0.001 to 2 percent of an oil-soluble polymer containing aliphatic hydrocarbon side chains having the formula CH,-(Cl-l,),,-CH where n is an integer of from 14 to 30, said polymer having a molecular weight of from 1,000 to 1,000,000 and being a member selected from the group consisting of (a) homopolymers of alkyl vinyl ethers or copolymers of alkyl vinyl ethers with one another and (b) copolymers of a mono-olefin and a dialkyl ester of an unsaturated dicarboxylic acid.

2. Composition of claim 1 in which the polymer is obtained by homopolymerization of an alkyl vinyl ether containing an aliphatic hydrocarbon chain or from 14 carbon atoms.

3. Composition of claim 2 in whichthe homoglymei;

is n-octadecyl vinyl ether.

4. Composition of claim 1 in which the polymer is obtained by copolymerization of a mono-olefin with a dialkyl ester of an unsaturated dicarboxylic acid, which ester contains aliphatic hydrocarbon chains or from 14 to 30 carbon atoms in the parts of the molecule derived from the alcohol.

5. Composition of claim 4 in which the copolymer is a copolymer of ethylene and di-n-octadecyl maleate.

6. A method of transporting waxy crude oil through a pipeline under reduced friction and without causing plugging of the pipeline comprising adding to the waxy crude oil from 0.001 to 2 percent of an oil-soluble polymer containing aliphatic hydrocarbon side chains having the formula CH -(CH ),,Cl-l where n is an integer of from 14 to 30; said polymer having a molecular weight of from 1,000 to 1,000,000 and being a member selected from the group consisting of (a) homopolymers of alkyl vinyl ethers or copolymers of alkyl vinyl ethers with one another and (b) copolymers of a monoolefin and a dialkyl ester of an unsaturated dicarboxylic acid.

Claims

2. Composition of claim 1 in which the polymer is obtained by homopolymerization of an alkyl vinyl ether containing an aliphatic hydrocarbon chain or from 14 carbon atoms.
3. Composition of claim 2 in which the homopolymer is n-octadecyl vinyl ether.
4. Composition of claim 1 in which the polymer is obtained by copolymerization of a mono-olefin with a dialkyl ester of an unsaturated dicarboxylic acid, which ester contains aliphatic hydrocarbon chains or from 14 to 30 carbon atoms in the parts of the molecule derived from the alcohol.
5. Composition of claim 4 in which the copolymer is a copolymer of ethylene and di-n-octadecyl maleate.
6. A method of transporting waxy crude oil through a pipeline under reduced friction and without causing plugging of the pipeline comprising adding to the waxy crude oil from 0.001 to 2 percent of an oil-soluble polymer containing aliphatic hydrocarbon side chains having the formula CH3-(CH2)n-CH2- where n is an integer of from 14 to 30, said polymer having a molecular weight of from 1,000 to 1,000,000 and being a member selected from the group consisting of (a) homopolymers of alkyl vinyl ethers or copolymers of alkyl vinyl ethers with one another and (b) copolymers of a mono-olefin and a dialkyl ester of an unsaturated dicarboxylic acid.